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Hi all

I pulled the head off a 850 engine that i have destined to go into a 64 van. Its on the std bore at the moment but has a lip at the top of the bores not too bad but realistically should have a rebore. Question is what are the options with pistons these days and at what cost?. Are there any other options than going for 850 pistons if so what are mods required and opinions on the outcomes

JP Pistons in Adelaide have new ones, they are very good quality.

except that i know of many sets that have failed. so many that a reputable mini parts and piston supplier will not use them.
it has something to do with the expansion rate of the alloy used, they haven't machined enough of a clearance for the piston skirt. so that when the engine gets warm the skirt "gripps" the bore and BANG, your looking to rebuild again.
you could get the pistons re machined, but for the price that they are asking, its cheaper to find a NOS set and ship them from europe.

just my 2c,
but i went through this ages ago trying to find good pistons, and ended up getting a NOS set of 20 thou over Hepolite pistons (that i still haven't used).

greyghost wrote:except that i know of many sets that have failed. so many that a reputable mini parts and piston supplier will not use them.
it has something to do with the expansion rate of the alloy used, they haven't machined enough of a clearance for the piston skirt. so that when the engine gets warm the skirt "gripps" the bore and BANG, your looking to rebuild again.
you could get the pistons re machined, but for the price that they are asking, its cheaper to find a NOS set and ship them from europe.

just my 2c,
but i went through this ages ago trying to find good pistons, and ended up getting a NOS set of 20 thou over Hepolite pistons (that i still haven't used).

Are you referring to JP's?

Your experience is interesting. I've used many of their pistons in various applications (not just BMC Stuff either) and found them quite good. Mind you if machining and preparation isn't right to start with, well you could hardly blame the piston. Sounds to me like the piston to bore clearance in your experience wasn't in accordance with JP's recommendations.

They couldn't be too bad, they have been around a very long time, if the pistons were all that bad, then they wouldn't be around.

NOS are not a bad option, but extraordinarily hard to come by.

One could always give a wee bit more clearance while boring the engine.

I have a friend who has an engineering company and when I last visited he had a few sets of NOS 850 pistons.

Let me know if your interested and I can ask him

Regards

Paul

Spider wrote:

greyghost wrote:except that i know of many sets that have failed. so many that a reputable mini parts and piston supplier will not use them.
it has something to do with the expansion rate of the alloy used, they haven't machined enough of a clearance for the piston skirt. so that when the engine gets warm the skirt "gripps" the bore and BANG, your looking to rebuild again.
you could get the pistons re machined, but for the price that they are asking, its cheaper to find a NOS set and ship them from europe.

just my 2c,
but i went through this ages ago trying to find good pistons, and ended up getting a NOS set of 20 thou over Hepolite pistons (that i still haven't used).

Are you referring to JP's?

Your experience is interesting. I've used many of their pistons in various applications (not just BMC Stuff either) and found them quite good. Mind you if machining and preparation isn't right to start with, well you could hardly blame the piston. Sounds to me like the piston to bore clearance in your experience wasn't in accordance with JP's recommendations.

They couldn't be too bad, they have been around a very long time, if the pistons were all that bad, then they wouldn't be around.

NOS are not a bad option, but extraordinarily hard to come by.

I agree Spider, I have used them in a number of engines, not just A series and they are fine. The set I use in our Historic Race car (Nb Cooper S) have been Teflon coated and withstand 8000rpm all day without any problems. I would also suggest if someone has had problems with JP pistions it would be more the builders/machinists fault rather than the piston. Repco/ACL here in Australia also made 850 pistions for many years and they are often available if you hunt around.